This invention relates to a method for analyzing carbonate salts in solutions. More particularly, this invention relates to an automated quantitative determination of the concentration of carbonate salts in aqueous solutions containing a large concentration of other salts.
An inorganic salt, such as sodium chloride, is used in many manufacturing processes. Such salt is normally obtained by direct mining or from brine wells which use water to dissolve the salt in the underground formations. This salt invariably contains substantial hardness impurities such as calcium and magnesium salts which will interfere with its use in the manufacturing processes. Therefore, it is necessary to remove as much as these impurities as possible before the salt is used in a manufacturing process.
One method of removing these hardness impurities is to dissolve the salt, if it is not already in solution from a brine well, and then treat it with sodium carbonate to precipitate out the water insoluble carbonate salts of the hardness impurities. In order to insure maximum removal of the impurities, it is necessary to analyze effluent from the treatment process so that an excess of sodium carbonate is used in the process.
Known prior art methods for the determination of carbonate salts in solutions comprise acidifying a sample to be analyzed to release an equivalent amount of carbon dioxide gas and then measuring the amount of carbon dioxide gas released by titrimetry, gravimetry, or infrared spectroscopy. The titrimetric and gravimetric methods are subject to substantial error due to interference by substances which, upon acidification of the sample, form acid gases or gases which upon contact with water form acids. The infrared method requires expensive equipment, has poor sensitivity and accuracy at low carbonate concentrations, and is affected by changes in temperature and moisture content of the liberated gases.